Systematic Study On DFT Prediction Of NMR Properties

Opposed to traditional wave-function methods, Density functional theory offers a cheap way to treat the correlation effects more efficiently; on the other hand, as a supplementary to experiments, theoretical calculation of NMR properties has become a useful tool for the interpretation of the experimental NMR data. In this paper, we systematically investigated the performance of density functionals on the prediction of NMR properties, and concluded that:●When the calculated NMR data are compared with the experimental data, caution has to be taken, as there are many sources of errors, such as the rovibratinoal correction, the intermolecular interactions and solvent effects, etc., which will degrade the comparison. An improper choice of the reference may result in misleading conclusions.●In contrast to the systematical overestimation of the magnetic shieldings predicted by MP2, DFT methods generally lead to too deshielded values. The source of errors may be traced back to the deficiency of the exchange functionals. We find that while the B88 and PBE exchange functionals are not recommended for the NMR calculations; the OPTX exchange functional consistently delivers the best absolute shieldings and chemical shifts.●The correlation functionals may be grouped into two classes. Class A, such as LYP, generally lowers the absolute shieldings and hence leads to an even deshielded value when combined with an exchange functional. On the other hand, Class B, such as PBE or PW91, generally increases the absolute shieldings, which partially compensates the deficiency of the exchange functional and hence leads to a better result in the prediction of NMR data.●We find that the OPBE and 0PW91 exchange-correlation functionals perform remarkably well along the whole set of systems, surpassing the standard non-density functional method, MP2, in many aspects. We conclude that OPBE or OPW91 is the best DFT functional currently available for the prediction of NMR data. Future work will be focus on the effect of current density dependency and the application of these functionals to the calculations of NMR spectroscopy of large molecules.